Hydraulic cement and method of producing same

ABSTRACT

GROUND MIXTURES OF CONVENTIONAL PORTLAND CEMENTMAKING COMPONENTS ARE MIXED WITH RELATIVELY SMALL AMOUNTS OF BORON-CONTAINING COMPONENTS, AND THE MIXTURES ARE BURNED AT KILN TEMPERATURES SUBSTANTIALLY BELOW THOSE NORMALLY UTILIZED TO FORM CLINKER. THE RESULTANT CLINKER IS MORE EASILY GRINDABLE THAN THAT PRODUCED IN CONVENTIONAL PROCESSES OF PORTLAND CEMENT PRODUCTION, AND THE CEMENT RESULTING FROM THE GRINDING OF THE CLINKER YIELDS CEMENTITIOUS PRODUCT POSSESSING SUBSTANTIALLY HIGH COMPRESSIVE STRENGTH IS EXHIBITED BY PORTLAND CEMENT MADE FROM THE SAME COMPONENTS IN THE ASSENCE OF THE BORON-CONTAINING COMPONENT.

AU 112v EX xR 3.6826669 LATER r-:rAL 3,382,669

HYDRAULIC CEMENT AND METHOD oF PRoDUcING SAME Filed Oct. 30, 1970 MASC.

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gelen/9d gwn/7 aar/ y United States Patent Olice 3,682,669 .Patented Aug. 8, 1972 3,682,669 HYDRAULIC CEMENT AND METHOD F PRODUCING SAME Thomas C. Slater, Sutter Creek, Calif., and Floyd C.

Hamilton, Jr., Louisville, Ky., assignors to The Flintkote Company, White Plains, N.Y. Continuation-impart of application Ser. No. 70,596, Sept. 8, 1970, which is a continuation of application Ser. No. 652,275, July 10, 1967. This application Oct. 30, 1970, Ser. No. 85,776

Int. Cl. C04b 7/38 US. Cl. 106--100 11 Claims ABSTRACT OF THE DISCLOSURE Ground mixtures of conventional portland cementmaking components are mixed with relatively small amounts of boron-containing components, and the mixtures are burned at kiln temperatures substantially below those normally utilized to form clinker. The resultant clinker is more easily grindable than that produced in conventional processes of portland cement production, and the cement resulting from the grinding of the clinker yields cementitious product possessing substantially higher compressive strength than is exhibited by portland cement made from the same components in the absence of the boron-containing component.

This application is a continuation-impart of our copending application Ser. No. 70,596 filed on or about Sept. 8, 1970 under Commissioners Order 824 O.G. l, which application is a continuation of application Ser. No. 652,275 led July 10, 1967 both now abandoned.

The tiled of art to which the present invention pertains is the making of portland-type cement.

The invention relates particularly to the production of portland cement and provides a method that, inter alia, results in a substantial savings in fuel and other operatingcosts and yields portland cement that forms products of substantially higher than normal compressive strengths.

In the conventional commercial practice for producing portland cement, certain proportions of crushed calcium carbonate, aluminum oxide, silicon dioxide and ferric oxide are pulverized, either in dry or slurry form. The ground mixture is burned in a kiln, usually of the rotary type, to form solid clinker that is pulverized with a small amount of gypsum to form the cement.

It is well recognized in the art that the operation of the kiln for forming clinker accounts for one of the largest single elements in the cost of producing portland cement.

The ground mixture must be burned at a temperature sutliciently high both to promote reaction in the solid state and to bring about fusion of the components, and thus to form clinker. The clinker is composed of calcium silicates, calcium aluminates, and calcium aluminate-ferrites, which constitute the hydraulically settable ingredients of cement formed by grinding the clinker.

Theoretically, the incipent fusion leading to the formation of the above-mentioned compounds can occur at a temperature of about 1338 C. (2440 F.). The formation of clinker is inuenced by the amount of liquid formed in the fusion, which is governed by the amount of aluminum oxide and iron oxide in the ground mixture.

In actual commercial operation utilizing rotary kilns at practical production rates, the residence or retention time of the material in the kiln at the above-mentioned minimum theoretical temperature is not long enough for the complete reaction to take place. Thus higher temperatures must be used to accelerate and complete the reaction between the components of the mix.

As indicated, for example, in the patents to Case, No. 2,004,463 of June 11, 1935, to Dyckerho, No. 2,970,- 925 of Feb. 7, 1961, and to Schifferle, No. 3,066,031 of Nov. 27, 1962, kiln temperatures of 1400 C. to 1450 C. (2550 F. to 2650 F.) are commonly utilized in cornmerical operations for forming cement clinker, although currently higher temperatures are usually used.

It is also well recognized in the prior art that the clinker produced by present commercial operations is diflicult to grind into a powder suitable for use as cement.

Stated in general terms, the present invention makes possible the production of portland cement clinker at temperatures substantially lower than those presently ernployed in commercial practice, and clinker that is more readily grindable than clinker produced in present commercial operations. Furthermore, the resultant ground cement forms concrete and other cementitious compositions that possess compressive strengths superior to those exhibited by portland cement as presently commercially produced.

The foregoing objects and advantages of the invention are achieved by 'ncorporatin into the round mix of ingredients conventi p portland cement, namely, limestone, silica, alumina and iron oxide, a relatively small portion of an additive material consisting essentially of a .n nent, and burning the mixture us ormed in a conventional portland cement kiln.

It has been found that the inclusion of such an additive as a component of the mix makes possible the formation of cement clinker at temperatures of about 2350 F. to about 2550 F. at about the same kiln retention time as in conventional processes. Clinker produced in this manner has improved grindability characteristics as indicated, for example, by less energy being needed to grind the clinker to a given surface area. The compressive strength of portland cement produced as described herein is substantially higher than the compressive strength of cement made from the same components but without the boroncontaining component.

The curve of the accompanying drawing shows the rela-A tionship between the kiln burning temperature and the amount of free lime in clinker made in accordance with this invention.

To produce portland cement according to this invention, there is rst formed by conventional procedures a pulverized mixture of raw materials composed of minerals containing calcium oxide` silicon dioxide, aluminum oxide and iron oxide. Limestone can be utilized as the source of calcium oxide. Silicon dioxide can be supplied in the form of sand, clay or shale. which can also be the source of aluminm oxide. The source of iron oxide can be mill scale, a by-product of steel mills, pyrite cinders, a by-product of sulfuric acid production, or iron ore. Iron oxide also is usually present in the raw materials used as the source of silicon dioxide and aluminum oxide. The raw materials are carefully proportioned and blended to maintain the relative proportions of the oxides within certain desired limits, in accordance with well-known practice, to produce cement having desired properties and characteristics. Typically, a portland cement has about 60% to 70% of lime as CaO, about 20% to 25% of silicate as SiO2, about 2% to 6% of iron oxide as Fe203, and about 3% to 8% of alumina as A12A3.

The pulverized mixture of the raw materials noramlly requires a burning temperature of the order of 2750 F. in the kiln to be transformed into a cement clinker `composed of desired percentage amounts of calcium silicate, calcium aluminate and calcium aluminate-ferrite reaction products. In accordance with the present invention, however, a cement clinker composed of the above-mentioned reaction products is formed at substantially lower burning temperatures in the kiln, namely, at temperatures of about 2350o F. to about 2550 F. This is achieved by incorporating a relatively small amount of a boron-containing material into the pulverized mixture of the raw materials fed to the kiln.

The boron-containing additive is intimately blended and intermixed with the raw pulverized mixture, or can be integround in the initial grinding process, and the material thus blended is fed to the kiln for burning into clinker.

The presence of the boron-containing component in the raw material fed into the kiln enables the raw material to be transformed into a highly satisfactory clinker at temperatures substantially lower than those normally required for mixtures without the boron-containing additive. Moreover, the resultant clinker possesses improved grindability and yields a pulverized cement that forms concrete and other cementitious compositions having superior compressive strengths.

During burning of the mixture, the rate and degree of completion of formation of the calcium silicate and calcium aluminate reaction products, particularly tricalcium silicate, is indicated by the amount of uncombined calcium oxide (CaO), so-salled free lime, present in the clinker. If the amount of free lime in the clinker exceeds about 2% by weight the resultant cement might be unsatisfactory, particularly in that such cement is susceptible to excessive expansion.

By including the boron-containing additive in the raw materials fed to the kiln, the clinker not only is formed at temperatures that are substantially below those conventionally required, but does not contain undesired amounts of free lime. Clinker having a satisfactory free lime content of about 2% or less can be obtained at kiln temperatures in the range of about 2350 F. to about 2550 F. At kiln temperature below that range, undesired amounts of free lime tend to be present in the clinker; at kiln temperatures above that range, the clinker might contain an undesired amount of free lime.

-The boron-containing additive 'used in the practice of this invention is an oxide of boron, a compound containing an oxide of boron or a compound that yields an oxide of boron at the temperature prevailing in a cement kiln. Examples of such boron-containing additives are boric acid anhydride, acids of boric acid anhydride, salts of bor-ic acid anhydride, polybon'c acids and polyborates such as diborates, triborates and tetraborates of ammonium, sodium, potassium, calcium, barium, strontium and magnesium, and boron-containing refined and unrened minerals or ores, including colemanite, and ulexite, danburite, pinnoite, ascherite and rasorite. The quantity of the boron-containing additive incorporated in the pulverized mixture of raw ingredients fed to the kiln is relatively small. An amount suicient to provide a B20, content in the range of about 1% to about 3% by weight of the pulverized mixture, preferably about 1.5% to about 2.5%, should be used, which amounts approximately can then be found in the clinker. In an actual embodiment of the'invention, a modified typical Type II portland cement pulverized mix was made up with the following components:

Percent Cataract limestone 72.58 Cataract shale 16.60 Winship clay 3.67 Pyrite cinders 2.39 Special additive #l 4.76

A. Modifier 100.00

Special Additive #l contained:

Percent SiOg 8.00 Fe203 0.19 A1203 0.35 CaO 14.66 MgO 2.67 NazO 5.19 K2O 0.23 B203 36 13 Ign Loss 32 57 Total 99 99 Thus, the mix had the following calculated composition:

Percent SiOs 22.55 A1203 5.82 Fe-OS 4.45 CaO 64.85 B203 1.86

Batches of the foregoing A. Modified mix were burned at various temperatures for a period of time equal to a typical portland cement kiln retention time at normal operation temperature of about 2800 F. The clinker prepared from each such batch contained the following amount of free lime:

Burn temperature, F. lPercent free lime The curve of the accompanying drawing is based on the above-tabulated data, and clearly shows that clinker having a desirably low level of free lime can be prepared at burn temperatures in the range of about 2350* F. to about 2550 F., a range of temperature markedly lower than the temperatures usually employed to make portland cement clinker having satisfactory low 'free lime content.

The production of a satisfactory cement clinker thus is possible at reduced kiln temperatures, and substantial savings in fuel cost as well as the other benefits can be obtained. Fuel savings that amount to the order of about 300,000 B.t.u. per barrel of cement clinker produced have been calculated. Also, by virtue of the lower temperatures utilized in the kiln operation longer kiln shell life and less frequent replacement of the refractory lining of the kiln are benefits that result in substantially reduced kiln maintenance cost. This cost reduction has been estimated to be of the order of about 10%.

In addition to and perhaps even more important than the foregoing advantages accruing from the use of the described boron-containing additives in accordance with this invention is the improvement thereby obtained with respect to the compressive strength of the resultant cement` Indicative of the superior strength characteristics of portland cement made from clinker produced in accordance with the invention are the data set forth herebelow.

As a control, a typical Type II portland cement mix without modification by an additive component of this invention was burned at about 2800 F. for about 30 minutes. The mix had the following raw materials and calculated compositions:

The free lime content of the clinker was 0.72%.

Compressive strength tests (ASTM Test C 109-64) were conducted on mortar cubes 2" x 2" x 2" made of the typical Type II Control cement described above and the A. Modified cement according to this invention from clinker burned at 2450 F. The cubes were kept in a cabinet in which the atmosphere was controlled at 70 F. and 100% relative humidity. The compressive strength of the cubes was tested after 7 and 28 days. The following table presents the results obtained and various factors involved in making the tests for the cements described above and also for another cement according to this invention (B. Modifed") to be described:

A. modified A. control 13. modified Clinlrersd temp. F.) J, 460 2. 800 2,660 B201 (percent). i. su 1.54 Free linie (percent) 0.77 0. 72 2. i7 Blniiie flneness. 3, 601 4, 106 3, 585 SO; added(perccut) 1. 62 1. x14 0. 50 Water (ce.) '.130 250 230 Initial sat (lir.:min.) 4:20 1:10 2:30 Final set hrnniin 7:00 8:40 7+ Compress va strung 7 days (psi.) 4.558 3 133 4,308 28 days (psi.) 9.375 5 7 9. '.68

As gypsum to make cement.

The B. Modified cement was prepared from a raw material mix containing 95.24 parts by weight of the A. Control cement raw material mix and 4.76 of Special Additive #1, and had a calculated composition as follows:

Percent SiO, 21.40 FCQO, AlgO, 5.60 CaO 63.57 B20, 1.54 Nago 0.26 Insol. 0.82 H2O 0.82

Total 98.31

Clinker was formed by burning the raw mix at 2550 F. for about 30 minutes, and had a free lime content of about 2.17%.

Compressive strength tests of steam-cured mortar cubes were made using a cement modified according to this invention (C. Modified") and an unmodified typical 'Upe H pipe cement as a control (B. Control").

The C. Modified cement was made from clinker formed at a burning temperature of about 2650 F. for about 30 minutes from a raw mix of 6.79 parts of Special Additive #2 (unrefined Kem County colemanite containing 34.11% 1320,) and 93.21 parts of the Type l1 control 6 mix set forth above. The clinker from this raw mix had a calculated analysis of:

Percent SiO, 22.63 A120, 5.71 F6203 Ca0 64.79 B203 1.87

C. Modified 99.37

The clinker had a free lime content of about 1.93%.

As a control cement, a commercial Type II portland pipe cement burned at about 2800 F. and having about 1.48% free lime was used. The control cement had an analyzed composition as follows:

Percent S10, 21.96 Fe203 3.28 A1203 4.80 CaO 64.87 S03* 2.38

B. Control" 97.29

Added as about 5% gypsum.

Cubes were made from mortar containing 1982 grams of sand and 793 grams of the B. Control cement and the C. Modified cement, and were cured for 20 hours in a cabinet mantained at 165 F. with steam. Thereafter, the cubes were placed in a cabinet at 70 F. and 100% relative humidity, and compressive strength tests were made on the cubes after 14 hours, 7 day and 28 days. The

following tabulation sets forth the strength and other factors associated with this test.

Compressive strength tests were also conducted on concrete cylinders (ASTM Test C 192-65) made from a Type 11 portland cement modified according to this invention (D. Modified) :ind an unmodified Type 11 cement (C. ControV). The clinker used to multe the D. Modified cement had an analysis of:

Percent SiO, 24.46 FCqO; 3.9() A130', 4.72 C 63.15 B20, 1.97

"D. Modified" 98.26

and contained 1.60% free lime after burning at about 2500 F. in a kiln for n usual itiln retention time of about 30 minutes. The raw material mix contained about 2.0% of B20, supplied ns boron trioxide. The C. Control cement, which contained 1.12% free lime, analyzed as:

Percent Slog 22.02 F6203 A1203 4.74 CaO 64.67 S03* 2.09

C. Control" 97.12

Added as about 5% gypsum.

C. Control D. Modified 7 days (psi.) 14 days (p.s.i.)-

From the foregoing data based on compressive strength tests, it is evident that cements made with the boroncontaining additives according to this invention have significantly greater strength, even though made at remarkcdly lower kiln burning temperatures, than Type Il portland cements.

It has also been found, quite surprisingly, that, cement clinker produced in accordance with the invention is more readily grindable than is clinker as normally produced, Le., without inclusion of the boron-containing component in the mix. Tests indicative of the grindability of the instant clinker as compared with clinker as normally produced were conducted in jar mills following procedures commonly accepted in the art, namely, by determining the Blaine surface area of the ground clinger at various stages of grinding. In specific terms, actual tests have shown that, by virtue o fthe improved grindability of clinker embodying this invention, production of the ground cement from such clinker can be increased approximately 140% to 200%.

For example, one cement made from clinker embodying this invention had a Blaine surface area of 3600 sq. cm. per gram after 4080 revolutions of a jar mill, whereas a comparable clinker as normally produced required 6120 revolutions to produce cement of substantially the same Blaine surface area (3590 sq. cm. per gram).

In another grindability test, the clinker of the D. Modified cement described above and a clinker corresponding thereto but produced without a boron-containing additive were ground. The latter clinker had the following analyzed composition:

Percent SiO, 23.52 F6203 A130, 4.70 CaO 66.46 Free Lime 0.92

D. Control" 99.32

3,000 grams of each clinker were ground with 3.5 cc. of Zeemill grinding aid, 6.0 cc. of water and 90 grams of gypsum for the D. Control and 7l grams of gypsum for the D. Modified. To achieve a Blaine surface area of about 4,000 sq. cm. per gram, a neness to which pipe cement commonly is ground, the D. Modified clinker required about 10,700 revolutions of the mill whereas the D. Control clinker required about 22,900 revolutions.

These grinding data demonstrate the remarkably irnproved grindability of clinker made in accordance with this invention.

Although a wide choice of boron-containing cornponents are available for use according to the invention, it is preferred to use boron trioxide (82,03), raw colemanite or refined colemanite.

It will be apparent to persons skilled in the art that numerous changes can be made in the ingredients, conditions and proportions set forth in the foregoing illustrative embodiments without departing from the invention a: described herein before and as defined in the appended c aims.

We claim:

1. A method of making portland cement having a free lime content below about 2% by weight of said portland cement which comprises forming an admixture of pulverized lime-containing mineral, silicon oxide-containing mineral, aluminum oxide-containing mineral, iron oxidecontaining mineral and an amount of a boron-containing substance suiiicient to provide at least about 1% by weight of B203 in said admixture, heating said admixture at a temperature above about 2350" F. to fuse the components of said admixture into clinkers, and grinding said clinkers.

2. A method according to claim 1 wherein the amount of said boron-containing substance as B203 is in the range of about 1% to about 3%.

3. A method according to claim 1 wherein the amount of said boroneontaining substance as B203 is in the range of about 1.5% to about 2.5%.

4. A method according to claim 1 wherein said boroncontaining substance is an oxide of boron, a compound containing an oxide of boron or a compound that yields an oxide of boron at the temperatures prevailing in a cement kiln.

5. A method according to claim 1 wherein said boroncontaining substance is boric oxide, calcium tetraborate or unrened colemanite ore.

6. A method according to claim 1 wherein said boroncontaining substance is boric oxide.

7. A method according to claim 1 wherein said boroncontaining substance is unrefined colemanite ore.

8. A method according to claim 1 wherein said pulverized minerals are limestone, silica, alumina and iron oxide.

9. A method according to claim 1 wherein said admixture is heated at below about 2750 F. to form said clinkers.

10. A method for increasing the grindability of sintered portland cement clinkers formed in a kiln by fusion of the mineral components of said cement and/or increasing the compressive strength of said cement, which comprises forming an admixture of pulverized lime-containing mineral, silicon oxide-containing mineral, aluminum oxidecontaining mineral, iron oxide-containing mineral and an amount of a boron-containing substance sufficient to provide at least about 1% by weight of B203 in said admixture, heating said admixture at a temperature above about 2350 F. to fuse the components of said admixture into clinkers, and grinding said clinkers.

11. A method for decreasing the operating temperature of a portland cement kiln and controlling the free lime content of portland cement clinkers at below about 2% by weight which comprises forming an admixture of pulverized lime-containing mineral, silicon oxide-containing mineral, aluminum oxide-containing mineral, iron oxide-containing mineral and an amount of a boron-containing substance suflicient to provide at least about 1% by weight of B20, in said admixture, and heating said admixture at a temperature in the range of from about 2350 F. to about 2550 F.. to fuse the components thereof into clinkers.

Refercneel Cited UNITED STATES PATENTS 2,709,661 5/1955 Dietz' 106--100 2,684,913 7/1954 West 106-89 1,852,595 4/1932 Steinour 106-89 FOREIGN. PATENTS 350,129 193i Great Britain I06-l00 284,294 1928 Great Britain 106-100 TOBIAS LEVOW, Primary Examiner W. T. SCOTT, Assistant Examiner U.S. C1. X.R.

(SEAL) Attest:

EDWARD M. FI.I5TCHIER,JR. Attesting Officer TUNITED STATES PATENT OFFICL/ CERTIFICATE OFA CORRECTION Patent No. 3 .682 669 Dated 8ll8j72 nvetods) Thomas C. Slater et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. '1, 1. 24, change "product" to products and.

1. 35, change "filed" to field C01. 2., 1. 59,

change "aluminm" toaluminum C01. 3', 1. 8, change.

1. 9, change "noramlly" to change "temperature" to temperatures and 1. 67, before "ulexite" delete "and"; Col. 4, 1. 10, change "Modifier" to Modified and 1. 64, after "operation" insert a comma; C01. 5, 1. 37, change "modified" to Modified and"'contro1" to Control Col. 6,

1. 33, change "day" to days and 1.- 41, change "finess" to fineness C01. 7, 1. 19, change "remark-J' to mark- 1. 21, after "that" delete the comma, 1. 30, .change "clinger" to clinke`r and 1. 32, change Signed and sealed this 9th day of January 1973.

. ROBERT GOTTSCHALK Commissioner of Patents FORM 704050 -I\O-69) UNITED STATES PATENT .OFFICE CERTIFICATE 0F- CORRECTION Patent No. 3 682,669 Dated 8)-[8j72 nvertods) Thomas C. Slater et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. l, l. 24, change "product" to products and' l. 35, change "filed" to field Col. 2., l. 59,

change "aluminm" to aluminum Col. 3', l. 8, change "A12A3" v to Al O l. 9, change "noramlly" to normally '59, change "temperature" to temperatures and l. 67, before "ulexite" delete "and"', Col. l, l. l0, change "Modifier" to Modified and l. 64, after w l "operation" insert a comma; Col. 5, l. 37, change "modified" to Modified andv "control" to Control Col. 6,

l'. 33, change "day" to days and l.l 4l, change "finess" to fineness Col. 7', l. 19, change remark" to markl'. 2l, after "that" delete the comma', l. 30, .change "clinger" to clinker and l. 32, change Signed and sealed this 9th day of January 1973.4

(SEAL) Attest:

.EDWARD M.FLITCHIER,JR.

. ROBERT GOTTSCHALK Attestng Officer Commissioner of Patents FORM F30-1050 (1D-69) USCOMM-DC 60376-F69 LLSA GOVERNMENT PRINTING OFFICE: |969 0-366-334 

